Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 60, Issue 14, Pages 3693-3699Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf204826e
Keywords
antioxidants; DPPH radical scavenging activity; density functional theory; bond dissociation enthalpy; spin density; ionization potential; proton affinity
Funding
- Council of Scientific and Industrial Research (CSIR), Government of India [NWP-53]
- UGC
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Structural, electronic, and energetic characteristics of tricin, tricin-4'-O-(erythro-beta-guaiacylglyceryl)ether (TEGE), and tricin-4'-O-(threo-beta-guaiacylglyceryl)ether (TTGE), isolated from Njavara rice bran have been studied using DFT to explain their experimentally determined radical scavenging activity (EC50 values) in comparison with known standards such as quercetin, myricetin, and catechin. Among the three mechanisms proposed for explaining the antioxidant activity, proton coupled-electron transfer (PC-ET), sequential proton loss electron transfer (SPLET), and electron transfer-proton transfer (ET-PT), our results support the second one. The O-H bond dissociation enthalpy (BDE) and the spin density on the oxygen with the radical character are excellent descriptors of radical scavenging activity. BDE (in kcal/mol) increased in the order myricetin (74.6) < quercetin < catechin (78.3) < tricin (81.5) < TTGE (90.6) < TEGE (91.1), while the EC50 increased exponentially with increase in BDE, 20.51, 42.98, 45.07, 90.39, 208.01, and 352.04 mu g/mL for myricetin, quercetin, catechin, tricin, TTGE, and TEGE, respectively.
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